Ask her to do a Urine Pregnancy test, f it comes negative and she still does not get her periods, she should meet her Gyne doc and take beta HCG test or a scan done to confirm/rule out the pregnancy. Avoid unprotected sex if you do not want risk of pregnancy, she can go for BCP an dyou should still continue to use condoms. Anesthesia is not known to upset mentrual cycles, she might be having some other problems if she is not pregnant, she will need a complete health check.